1. Field of the Invention
The invention relates to agricultural combines and, more particularly, relates to a method and apparatus for selectively controlling a threshing rotor of an agricultural combine by controlling the operation of a hydro-mechanical drive system for the rotor.
2. Discussion of the Related Art
Agricultural combines or “combine harvesters” are well-known for harvesting crops such as corn, soybeans, and wheat. The typical combine includes a self-propelled chassis supported on the ground via driving and driven wheels. A replaceable harvesting head is mounted on the front of the chassis for harvesting the crop of interest. The combine is operable to feed the harvested grain from the head to an internal threshing and separating system that separates the grain from stalks, pods, cobs, etc. (collectively referred to herein as “chaff”) and that transfers the grain to an on-board storage hopper. The stored grain can be periodically transferred to a wagon or the like by an auger mounted on the chassis adjacent the storage hopper.
The threshing and separating system of the typical combine includes at least one threshing rotor, a concave, a grain pan, sieves and fans. Of these components, the rotor is of the most importance for purposes of the present invention. (The rotor(s) will hereafter be referred to in the singular for the sake of convenience, it being understood that the problems addressed by the invention, and the invention itself, are equally applicable to single rotor and multiple rotor systems). Torque is typically transferred to the rotor directly from the engine by a belt drive system that is engaged by a mechanical clutch. However, in order to increase the amount of crop processed by the combine, the size, weight and power consumption of the rotor are being increased to levels above the tolerances of belt driven technology. It is difficult to accelerate such a rotor from rest, particularly under certain crop conditions, because accelerating the high-inertia rotor places high stresses on both the belt drive and the clutch used to engage the belt drive. The loads imposed on the rotor after it is accelerated up to speed also can vary dramatically. The stress on the clutch and belt can be severe, resulting in early clutch and belt failure. Additionally, there are instances in which the combine encounters a “slug” condition in which the operator may determine that the crop is lodged between the rotor and concave. It may be desirable in this situation to permit the operator to control the rotor to reverse the direction of rotor rotation to deslug the rotor.
So-called “split-torque” or “hydro-mechanical” transmissions have been proposed to address these and other problems encountered when driving a threshing rotor. For instance, U.S. Pat. No. 5,865,700 to Horsch discloses a hydro-mechanical drive system including an engine and a hydrostatic motor which derives its power from the engine. A single clutch controls the input of the engine power and input of the hydrostatic motor power. However, if input from the hydrostatic motor is not precisely synchronized with input of the engine, the input of the hydrostatic motor could brake the engine, possibly damaging to the engine.
U.S. Pat. No. 6,247,695 to Hansen discloses a combine having a hydro-mechanical transmission that is designed to alleviate the problems exhibited by Horsch and other hydro-mechanical transmissions by accelerating the rotor by gradually engaging the clutch. More specifically, in the system disclosed in the Hansen patent, an engine drives a wet clutch and a hydrostatic motor. The output of the motor drives the sun gear of a hydro-mechanical planetary drive, and the output of the clutch drives the ring gear of the same drive. A carrier of the planetary drives the rotor. The transmission is controlled by a microcomputer that receives signals from an engine speed sensor and a rotor speed sensor. The microcomputer also transmits controlling signals to the hydrostatic pump's swash plate and to a clutch valve to control clutch engagement. The microcomputer can also send a signal to brake the ring gear while reversing the direction of the hydrostatic pump motor to allow it to act as a reverser for the rotor to effect a deslugging operation. The microcomputer also can receive signals from the rotor speed sensor to control a supply valve for the clutch to ensure that the clutch input and output are synchronous.
The hydro-mechanical rotor drive system disclosed in the Hansen patent is only partially effective at addressing the problems encountered by the prior art. For instance, the system relies on gradual engagement of the wet clutch to accelerate the rotor from rest to the commanded speed. That is, hydraulic pressure in the wet clutch is increased progressively as rotor speed increases from rest until the clutch input and output are synchronous.
The ring to frame brake remains disengaged at this time, and torque from the hydraulic motor is supplied only to provide any necessary make up torque between that provided by the engine and that required to place the rotor in its desired instantaneous operating state, i.e., to accelerate the rotor at the desired rate and/or to maintain rotor velocity constant during steady state operation of the machine. This control operation places considerable strain on the wet clutch, shortening the life of the clutch and the belt. In addition, clutch engagement is controlled by switching the flow of hydraulic fluid hence effectively rendering the clutch an ON/OFF clutch that is either essentially fully-engaged or essentially fully-disengaged. In addition, the Hansen patent controls rotor speed strictly in dependence on prevailing engine speed. Hansen considers this control to be advantageous because decreases in motor speed resulting from a slug condition will alert the operator that the machine is overloaded and, theoretically, cause the operator to lower the rotor power in order to allow the engine to recover. However, this technique results in frequent, potentially undesired variations in rotor speed, particularly when engine speed changes occur through factors other than a rotor slug condition.
In addition, rotor speed in Hansen is varied strictly as a function of hydraulic and mechanical motor speeds. Depending on the circumstances, the hydrostatic motor may have to supply substantial positive or negative make-up torque to make up a large difference between commanded rotor velocity and the actual engine velocity. For instance, at a low nominal engine speed and a high commanded rotor velocity, torque transfer may be divided generally equally between the engine and the hydrostatic motor. This “split delivery” is relatively inefficient because a relatively large percentage of power must be supplied by the relatively inefficient hydrostatic motor rather than more efficient mechanical motor. The required make-up torque could be reduced substantially if the speed range of the system's gearing could be altered to assure that an engine operating at a particular speed always drives the rotor at or reasonably near the commanded rotor velocity.
The need therefore has arisen to provide a method of controlling operation of a threshing rotor of an agricultural combine so as to minimize clutch wear.
The need has also arisen to provide a method of improving the torque transfer efficiency of a threshing rotor drive system throughout the operational range of the rotor.
The need has also arisen to provide a method of deslugging a threshing rotor without sacrificing the efficiency of other operational aspects of the system.
The need therefore has arisen to provide a simple, reliable, durable, and efficient hydro-mechanical threshing rotor drive system for an agricultural combine.